The present invention relates to providing a new and improved temperature control system for internal combustion engines having a cooling liquid therein. In a typical vehicle having a liquid cooled internal combustion engine, the fan clutch is either disengaged completely with two clutch faces separated or fully engaged with the two clutch faces transmitting power across the clutch face interface without any slippage between the faces. Usually, the clutch faces are engaged or disengaged pneumatic or electromagnet actuators. When the clutch is engaged in a large truck, considerable horsepower is used to drive the fan. Where the fan is a 32" diameter fan, the horsepower used to drive the fan can be as much as 40-80 horsepower for large trucks which have engines in the range of 200-600 horsepower. On the other hand, when the fan is fully off, the fan is disconnected from the power drive from the engine's crankshaft. The fan is free-wheels and does not contribute to cooling of the engine. In these particular type of on/off electromagnetic and air-actuated fan clutches, the fan is disconnected when the engine is cold or is being adequately cooled, for instance when air is forced rapidly through the radiator by high speed travel of the vehicle.
The control system for the fan clutch includes a thermostat, which monitors the engine or the cooling fluid temperature and tries to maintain the temperature within a predetermined range--for example, 181.degree. F.-190.degree. F.; and the control system includes a speed measuring sensor which disengages the clutch when the vehicle speed reaches a set speed--for example, 30 mph. At 30 mph, it is assumed that there is sufficient ram air flow across the radiator to cool the engine without operation of the fan.
With large trucks which are running at 2,100 rpm and which use 40-80 horsepower to drive a large fan having a large movement of inertia, e.g., a 32-inch diameter fan, it is necessary to build a fairly substantial fan clutch to withstand the shock of suddenly engaging and rotating the inertia of a stationary, driven clutch face and its attached fan quickly to its full rotational speed. Consequently, current fan clutches are quite large and substantially made to withstand such shock loads.
In addition to such load problems from the large movement of inertia, another problem with current fan clutch systems is that of chattering, i.e., an abrupt, recurring, on/off engagement of the clutch fan faces due to a rapid opening and closing of a thermostat switch trying to maintain the cooling temperature between 181.degree. F. and 190.degree. F. Typically, the on/off thermostat has a variation of seven degrees (7.degree. F.) with a tolerance of plus or minus two (2.degree. F.) degrees between turning on or shutting off. In some adverse, ambient conditions of operation, this cycling goes back and forth as many as 50 times per hour, thereby causing wear and tear on clutch faces, when they are being repeatedly mechanically engaged and disengaged.
When the clutch is operated by an air pressure system from the truck's compressed air system, other problems arise. That type of clutch uses compressed air to operate the clutch actuator system. It is difficult to keep the compressed air clean. The truck compressor air is usually too dirty to be used directly to operate the fan clutch actuator system. The air must first be cleaned by bubbling it through oil in an oil filter which traps dirt from the air. If the oil in the filter becomes dirty, it will pass contaminants. The still-contaminated air may compromise a downstream pressure regulator resulting in an insufficient air pressure for operating the clutch actuator, e.g., the air pressure may drop below 70 pounds and not provide sufficient force to operate the clutch. If the fan is not operated, the temperature can reach 450.degree. F. at the fan blades. The plastic fan may ignite setting the entire truck afire. Pneumatic fan clutch systems are bulky and expensive.
With the current fan clutch systems, the driver turns on the air conditioning system for the truck and the fan clutch is automatically engaged to turn the fan at full speed even though full fan speed may not be needed for adequate cooling of the engine. For example, the ram air flowing through the radiator at high vehicle speeds could be sufficient to keep the air conditioner and the truck engine temperature low enough without the fan. While engaging the fan clutch when the air conditioner switches on ensures that the air conditioning system and the engine are kept cool at all times, it wastes energy.
Current fan clutch systems in trucks have the fan mounted fairly high which keeps the nose or the front end of the vehicle high. Truck manufacturers and truck drivers want to lower the truck nose for streamlining the aerodynamics of the truck and to provide a better view of the road. In some trucks, the radiator has been turned on its side so that it is a side-flow radiator in order to lower the tractor nose profile. In some tractors, there is insufficient space to position a large fan on its side and place it between the frame rails for the vehicle. Hence, the fan cannot be side-mounted to drop it lower.
These electromagnetic and pneumatically-clutched fans are not rapidly connected to the engine crankshaft because the crankshaft vibrates at a natural frequency that causes the engaged faces of the clutch plates to vibrate against one another and to wear quickly. Thus, most trucks in the United States have a fan belt drive from the crankshaft to the fan clutch which is located above the crankshaft. A fan belt drive, however, takes space, and the belt is subject to failure. The fan belt system also adds cost to the engine cooling system. Although many truck manufacturers would prefer to lower the radiator and fan to the location of the crankshaft, they are unable to do so because of the crankshaft vibrations and the space needed for the fan belt drive of the fan clutch and fan.
Some vehicles, principally in Europe, have a fan clutch which is mounted on the crankshaft and which is always partially engaged to transfer a certain amount of power to the fan. For example, at least 40% of the power to turn the fan to full speed needed and up to 90% of the power needed to turn the fan at full speed. This clutch never transfers 100% of the power needed, and this clutch is never totally disengaged such that the fan can be free-wheeling. This particular type of clutch also has a vibration isolator which to some extent serves to dampen or isolate vibrations at the fan clutch from the crankshaft vibrations. If the vibration isolator wears out allowing vibration to be transmitted, the clutch will wear out in only a few days.
Such a constantly engaged fan wastes fuel. If the fan consumes a maximum of 40-80 horsepower, and the fan never uses less than 40% of its input power, this means that at least 16 horsepower is being consumed that may not be needed. At the higher end, 40% of the 80 horsepower is 32 horsepower which may not be needed but it is always being expended. This unneeded expenditure of energy results in fuel inefficiencies for vehicles having such fan clutches.
Similarly, in most automobiles, the fan runs continually while the vehicle engine is running. Such continuous fan operation wastes fuel, particularly when the engine is moving at a sufficient speed to provide ram air which would cool the engine; or when the engine is cold and there is no need for any further cooling by a fan.
It will be appreciated that pneumatic or electromagnetic actuators for bringing the clutch faces into engagement are relatively complex, occupy considerable space, heavy and costly. The controls using the thermostat on and off switch as well as a speedometer sensor on/off switch provide the most rudimentary information because more information would not enable any more sophisticated thermal management due to the fact that the clutch cannot be modulated in its torque transfer and thereby achieve proportional control of engine temperature. Also, it will be appreciated that the amount of horsepower being used for a fan cooling system is very substantial in that great fuel economy savings could be accomplished by having an improved fan clutch and control system for the internal combustion engine cooling.